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Civilians have sought shelter at the UN mission outside Juba in South Sudan

The UK has sent an aircraft to South Sudan to evacuate Britons amid fighting following a reported coup attempt.

The Foreign Office said British nationals in the country should make contact if they wish to leave from Juba airport on Thursday.

There has been fighting this week in the capital Juba, and President Salva Kiir has declared a night-time curfew.

The Foreign Office has temporarily withdrawn some staff and dependants from the British embassy in Juba.

Some commercial flights have resumed at Juba airport.

A Foreign Office spokeswoman said: "To date over 150 British nationals have contacted us, many of whom want help leaving the country."

These included some non-embassy staff, the spokeswoman added.

The Foreign Office said its embassy in Juba remained open although the situation was being reviewed on a "constant basis".

It has advised against all travel to within 40km of South Sudan's northern border with Sudan, Jonglei State and Juba, and all but essential travel to the rest of South Sudan.

President Kiir has accused ex-vice-president Riek Machar of staging the coup - a claim he denies.

The UN called for political dialogue to end a crisis that has left hundreds dead and sparked fears of a civil war.

On Wednesday, Mr Kiir said he was willing to enter into talks with Mr Machar but that he did not know what the result would be.

The United Nations has estimated that up to 500 people have been killed in fighting between rival factions following a coup attempt against the president by soldiers loyal to his former deputy.

Secretary general Ban Ki-moon said that about 20,000 people had taken refuge with the UN in Juba.

British nationals wanting to leave Juba should contact the Foreign Office as soon as possible on +44 207 008 1500 or by email at crisis@fco.gsi.gov.uk.

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Both Sudan and the South are reliant on oil revenue, which accounts for 98% of South Sudan's budget. They have fiercely disagreed over how to divide the oil wealth of the former united state - at one time production was shutdown for more than a year. Some 75% of the oil lies in the South but all the pipelines run north.

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The two Sudans are very different geographically. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest.

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Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.

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In the Sudanese states of Khartoum, River Nile, and Gezira states, two-thirds of people have access to piped drinking water and pit latrines. In South Sudan, boreholes and unprotected wells are the main drinking sources. More than 80% of South Sudanese have no toilet facilities.

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Conflict and poverty are the main causes of food insecurity in both countries. In Sudan, many of the residents of war-affected Darfur and the border states of Blue Nile and South Kordofan depend on food aid. The UN said about 2.8m people in South Sudan would require food aid in 2013.